This is the application for the fourth renewal of the UCLA Chemistry-Biology Interface (CBI) Predoctoral Training Program, which has been funded since 1993. The objective of the UCLA CBI Training Program is to educate the scientists who will lead research and training at the interface between chemistry and biology in the decades to come. The rational for needing a CBI program at UCLA is that despite interactions and collaborations across disciplines, Ph.D. training is often traditional and insular in each department, emphasizing courses and training in a narrow specialty. Although deep training within a discipline is necessary and important, the next generation of scientists will also need to be educated across disciplines to be maximally effective in this modern era. The UCLA CBI Program provides this by breaking down the isolation between departments, and immersing trainees in state-of-the-art interdisciplinary research that spans the interface of chemistry and biology. Participating trainees come from all research areas of the Department of Chemistry and Biochemistry, as well as from the Departments of Molecular & Medical Pharmacology, Microbiology, Immunology & Molecular Genetics, Molecular, Cell & Developmental Biology, Chemical Engineering, and Bioengineering, and from the Molecular Biology Institute, Neuroscience Program, and Access Program. Graduate student trainees are involved in research that (1) has a strong organic, physical, or analytical chemistry component and (2) addresses significant unsolved problems at the Chemistry/Biology interface. The major requirements of the program are (1) completion of Chem205A, an interdisciplinary graduate level course entitled Introduction to Chemistry of Biology, Chem205B, Issues on the Chemistry-Biology Interface a course designed to provide trainees with information about techniques that can be implemented in their research, and Chem203B, ethics training. (2) Students will also participate in Chem206, a weekly luncheon seminar course consisting of intensive review and discussion of cutting- edge research at the chemistry biology interface and trainee presentations, and (3) participation in a cross-disciplinary research internship. The training program is for three years and twelve predoctoral trainees are requested to meet some of the strong demand for this training program. The program converts brilliant chemists who are amateurs in biology into chemists who can identify and solve the most important problems in biology and who are highly collaborative with biologists. It also turns the biologist using a chemical technique as a black box into an expert who contributes to the development of chemical methods to study biology, can identify new chemical approaches to solve their biological problems, and who are comfortable collaborating with chemists. This coherent and interactive training program also has significantly strengthened the scientific and educational environment at UCLA.